Pavlov's Dog

Ivan Pavlov was one of the most prominent scientists in the world at the beginning of the 20th Century. His discovery of classical conditioning actually came late in his career. For decades, Pavlov did research on digestive reflexes: the biological processes of digestion triggered by inputs to the stomach. He was an exceptionally good researcher who received a Nobel Prize for his research.

When Pavlov delivered his acceptance speech at the Nobel Prize banquet in 1904, he surprised the crowd. He lectured about something he accidentally discovered while doing his digestion research—classical conditioning—rather than the digestion research that won him the prize. Pavlov announced that he had discovered conditional reflexes, reflex responses occurring as the result of learning.

Pavlov giving his Nobel Prize speech in 1904.

The discovery occurred when Pavlov connected a clear tube to the dog's salivary gland in the cheek, so he could measure the amount of salivation that took place after food was placed in the mouth. A similar set-up (that of Pavlov's co-worker G.F. Nicolai) is shown below.

The dog was restrained in a harness with its head held still so the tube would not be ripped out. The researcher puffed meat powder into the dog's mouth to start the digestive process. Dogs salivate ("slobber") when they eat, so the meat powder stimulated lots of saliva. The saliva dripped out of the tube into a beaker where it could be measured.

A dog with a tube connected to its salivary gland

For what work was Pavlov awarded the Nobel Prize? How did he surprise the audience? In what sense did Pavlov's dog respond to a psychological stimulation?

With a set-up like this, Pavlov probably could not help but notice that dogs anticipated their meals. When Pavlov or an assistant entered the laboratory carrying meat powder, the saliva began dripping out of the tube. Pavlov realized this was significant. A biological reflex (salivation) was being modified by something psychological, namely, anticipation. In Pavlov's terminology, the dog's prediction was a form of "psychic stimulation" that activated the reflex. How could this happen? Reflexes were biological, yet the reflex was influenced by psychological factors.

Ivan Pavlov

Pavlov next devised a systematic version of his accidental observation. He (1) sounded a tone, and then (2) fed the dog meat powder. After a few repetitions, the dog started salivating when it heard the tone, even before the meat powder entered its mouth.

Pavlov was in his late 40s, but he changed his research program quickly to focus on this phenomenon and continued studying it until shortly before his death at age 87. In 1906 he followed up on his Nobel Prize speech by publishing an article in the American journal Science, summarizing his findings. The Science article was titled, "The Scientific Investigation of the Psychical Faculties or Processes in the Higher Animals." In those days, psychical meant the same thing as psychological.

What was Pavlov's one-word label for classical conditioning? What research did Watson do, using Pavlov's method?

Pavlov had a one-word label for classical conditioning. He called it signalization. That is not a bad label for classical conditioning, which occurs when a signal triggers a reflex-like response.

In America, John B. Watson (the "father of behaviorism" described in Chapter 1), heard about Pavlov's research. Watson used Pavlovian conditioning in his own research. For example, he carried out many studies of the fingertip withdrawal reflex. Watson would ring a bell then quickly shock a person's fingertip with a small amount of electricity, causing involuntary withdrawal of the fingertip. Soon the person would withdraw his or her fingertip whenever the bell rang.

Pavlov's dog and Watson's fingertip illustrate the basic pattern found in all classical conditioning. An organism learns that a signal predicts the activation of a reflex. After learning this, the organism reacts to the signal with an anticipatory response similar to the reflex response